在哪里初始化 Xamarin.iOS 应用程序中实例化的 PCL？

Question

I'm working on a Xamarin application, which I will at first have working on iOS, but plan to later expand to Android and other mobile platforms.

As such, I'm trying to keep as much common code in PCLs as possible.

My question: what is the best practise - in Xamarin.iOS for now - to initialize any dependent PCL code?

For now I have it in the RootViewController inside ViewDidLoad()

public override void ViewDidLoad()
{
    base.ViewDidLoad();
    _engine = new MyEngine();
    View = new MainView(_engine);
}

Is this the right spot? I'd considered putting it in the ctor for the RootViewController , but there's a fair bit going on in the initialization code, which thus ran against "don't put heavy duty init code into a constructor".

Things that happen are:

• Load app settings
• If app is run for first time ever, load basic defaults
• Initialise other PCL libraries, such as a TextToSpeech module, a state engine (hence the name of the class above), etc
• Prepare a data grid based on XML or JSON input

Alternately, I though it should possibly go into the AppDelegate section, but that didn't sound right.

I'm still fairly new to mobile app dev in general and Xamarin in specific, though I've done C# native code for Windows for years. I just want to make sure I follow best practises, but there doesn't seem to be a "thou shalt" in this case.

Edit: I've extracted the solution based on @wishmaster's suggestions.

Answer 1

For iOS the Appdelegate method is the best place for initialization code. The appdelegate also provides multiple delegate methods to give you feedback on application lifecyle events such as the method " DidFinishLauchingWithOptions " . if you have a lot of data to download or long running tasks that your app depends on I would suggest you take a look backgrounding for iOS . A technique I have also used is for my first viewcontroller on IOS (or activity on Android) to display a splash screen and a loading indicator while i run some code to refresh the cache.

Answer 2

Using @wishmaster's pointers, this solution works like a charm:

In AppDelegate.cs

// in the global section put any data you may make available elsewhere
private var _engine;
public Engine => _engine;

public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
    /*
     * Do whatever init needs to happen here, if you need to make this
     * available elsewhere, ensure you have properties or accessors,
     * as above.
     */
    _engine = new MyEngine();
    return true;
}

Then in RootViewController.cs using a similar approach to these examples in Obc-C or Swift you can access the information through a property pointing at the AppDelegate.

var myappdelegate = UIApplication.SharedApplication.Delegate as AppDelegate;
var engine = myappdelegate.Engine;
View = new MainView(engine);

The result resulted in a snappier start up of the application, because the initialisation now happens during the splash screen and no longer between splash screen and appearance of the UI.